840 research outputs found
The evaluation of a shuttle borne lidar experiment to measure the global distribution of aerosols and their effect on the atmospheric heat budget
A shuttle-borne lidar system is described, which will provide basic data about aerosol distributions for developing climatological models. Topics discussed include: (1) present knowledge of the physical characteristics of desert aerosols and the absorption characteristics of atmospheric gas, (2) radiative heating computations, and (3) general circulation models. The characteristics of a shuttle-borne radar are presented along with some laboratory studies which identify schemes that permit the implementation of a high spectral resolution lidar system
Fast Fourier Optimization: Sparsity Matters
Many interesting and fundamentally practical optimization problems, ranging
from optics, to signal processing, to radar and acoustics, involve constraints
on the Fourier transform of a function. It is well-known that the {\em fast
Fourier transform} (fft) is a recursive algorithm that can dramatically improve
the efficiency for computing the discrete Fourier transform. However, because
it is recursive, it is difficult to embed into a linear optimization problem.
In this paper, we explain the main idea behind the fast Fourier transform and
show how to adapt it in such a manner as to make it encodable as constraints in
an optimization problem. We demonstrate a real-world problem from the field of
high-contrast imaging. On this problem, dramatic improvements are translated to
an ability to solve problems with a much finer grid of discretized points. As
we shall show, in general, the "fast Fourier" version of the optimization
constraints produces a larger but sparser constraint matrix and therefore one
can think of the fast Fourier transform as a method of sparsifying the
constraints in an optimization problem, which is usually a good thing.Comment: 16 pages, 8 figure
TrES-2: The First Transiting Planet in the Kepler Field
We announce the discovery of the second transiting hot Jupiter discovered by
the Trans-atlantic Exoplanet Survey. The planet, which we dub TrES-2, orbits
the nearby star GSC 03549-02811 every 2.47063 days. From high-resolution
spectra, we determine that the star has T_eff = 5960 +/- 100 K and log(g) = 4.4
+/- 0.2, implying a spectral type of G0V and a mass of 1.08 +0.11/-0.05 M_sun.
High-precision radial-velocity measurements confirm a sinusoidal variation with
the period and phase predicted by the photometry, and rule out the presence of
line-bisector variations that would indicate that the spectroscopic orbit is
spurious. We estimate a planetary mass of 1.28 +0.09/-0.04 M_Jup. We model B,
r, R, and I photometric timeseries of the 1.4%-deep transits and find a
planetary radius of 1.24 +0.09/-0.06 R_Jup. This planet lies within the field
of view of the NASA Kepler mission, ensuring that hundreds of upcoming transits
will be monitored with exquisite precision and permitting a host of
unprecedented investigations.Comment: Accepted for publication in ApJL. 15 pages, 2 figure
A 96-well DNase I footprinting screen for drug–DNA interactions
The established protocol for DNase I footprinting has been modified to allow multiple parallel reactions to be rapidly performed in 96-well microtitre plates. By scrutinizing every aspect of the traditional method and making appropriate modifications it has been possible to considerably reduce the time, risk of sample loss and complexity of footprinting, whilst dramatically increasing the yield of data (30-fold). A semi-automated analysis system has also been developed to present footprinting data as an estimate of the binding affinity of each tested compound to any base pair in the assessed DNA sequence, giving an intuitive ‘one compound–one line’ scheme. Here, we demonstrate the screening capabilities of the 96-well assay and the subsequent data analysis using a series of six pyrrolobenzodiazepine-polypyrrole compounds and human Topoisomerase II alpha promoter DNA. The dramatic increase in throughput, quantified data and decreased handling time allow, for the first time, DNase I footprinting to be used as a screening tool to assess DNA-binding agents
WFPC2 Observations of the Cooling Flow Elliptical in Abell 1795
We present WFPC2 images of the core of the cooling flow cD galaxy in Abell
1795. An irregular, asymmetric dust lane extends 7 \h75 kpc in projection to
the north-northwest. The dust shares the morphology observed in the H
and excess UV emission. We see both diffuse and knotty blue emission around the
dust lane, especially at the ends. The dust and emission features lie on the
edge of the radio lobes, suggesting star formation induced by the radio source
or the deflection of the radio jets off of pre-existing dust and gas. We
measure an apparent R significantly less than 3.1, implying that the
extinction law is not Galactic in the dust lane, or the presence of line
emission which is proportional to the extinction. The dust mass is at least
2 M\solar\ and is more likely to be 6.5 M\solar.Comment: 14 pages, LaTeX, Figure 4 included, Postscript Figs. 1-3 available at
ftp://astro.nmsu.edu/pub/JASON/A1795/, accepted for publication in ApJ
Letter
UV-dropout Galaxies in the GOODS-South Field from WFC3 Early Release Science Observations
We combine new high sensitivity ultraviolet (UV) imaging from the Wide Field
Camera 3 (WFC3) on the Hubble Space Telescope (HST) with existing deep
HST/Advanced Camera for Surveys (ACS) optical images from the Great
Observatories Origins Deep Survey (GOODS) program to identify UV-dropouts,
which are Lyman break galaxy (LBG) candidates at z~1-3. These new HST/WFC3
observations were taken over 50 sq.arcmin in the GOODS-South field as a part of
the Early Release Science program. The uniqueness of these new UV data is that
they are observed in 3 UV/optical (WFC3 UVIS) channel filters (F225W, F275W and
F336W), which allows us to identify three different sets of UV-dropout samples.
We apply Lyman break dropout selection criteria to identify F225W-, F275W- and
F336W-dropouts, which are z~1.7, 2.1 and 2.7 LBG candidates, respectively. Our
results are as follows: (1) these WFC3 UVIS filters are very reliable in
selecting LBGs with z~2.0, which helps to reduce the gap between the well
studied z~>3 and z~0 regimes, (2) the combined number counts agrees very well
with the observed change in the surface densities as a function of redshift
when compared with the higher redshift LBG samples; and (3) the best-fit
Schechter function parameters from the rest-frame UV luminosity functions at
three different redshifts fit very well with the evolutionary trend of the
characteristic absolute magnitude, and the faint-end slope, as a function of
redshift. This is the first study to illustrate the usefulness of the WFC3 UVIS
channel observations to select z<3 LBGs. The addition of the new WFC3 on the
HST has made it possible to uniformly select LBGs from z~1 to z~9, and
significantly enhance our understanding of these galaxies using HST sensitivity
and resolution.Comment: Accepted for publication in ApJ (24 pages, 7 figures
The Size Evolution of Passive Galaxies: Observations from the Wide Field Camera 3 Early Release Science Program
We present results on the size evolution of passively evolving galaxies at
1<z<2 drawn from the Wide Field Camera 3 Early Release Science program. Our
sample was constructed using an analog to the passive BzK selection criterion,
which isolates galaxies with little or no on-going star formation at z>1.5. We
identify 30 galaxies in ~40 square arcmin to H<25 mag. We supplement
spectroscopic redshifts from the literature with photometric redshifts
determined from the 15-band photometry from 0.22-8 micron. We determine
effective radii from Sersic profile fits to the H-band image using an empirical
PSF. We find that size evolution is a strong function of stellar mass, with the
most massive (M* ~ 10^11 Msol) galaxies undergoing the most rapid evolution
from z~2 to the present. Parameterizing the size evolution as (1+z)^{-alpha},
we find a tentative scaling between alpha and stellar mass of alpha ~ -1.8+1.4
log(M*/10^9 Msol). We briefly discuss the implications of this result for our
understanding of the dynamical evolution of the red galaxies.Comment: 11 pages, 7 figures, 4 tables. Submitted to Ap
Stellar Populations of Lyman Break Galaxies at z=1-3 in the HST/WFC3 Early Release Science Observations
We analyze the spectral energy distributions (SEDs) of Lyman break galaxies
(LBGs) at z=1-3 selected using the Hubble Space Telescope (HST) Wide Field
Camera 3 (WFC3) UVIS channel filters. These HST/WFC3 observations cover about
50 sq. arcmin in the GOODS-South field as a part of the WFC3 Early Release
Science program. These LBGs at z=1-3 are selected using dropout selection
criteria similar to high redshift LBGs. The deep multi-band photometry in this
field is used to identify best-fit SED models, from which we infer the
following results: (1) the photometric redshift estimate of these dropout
selected LBGs is accurate to within few percent; (2) the UV spectral slope
(beta) is redder than at high redshift (z>3), where LBGs are less dusty; (3) on
average, LBGs at z=1-3 are massive, dustier and more highly star-forming,
compared to LBGs at higher redshifts with similar luminosities
(0.1L*<~L<~2.5L*), though their median values are similar within 1-sigma
uncertainties. This could imply that identical dropout selection technique, at
all redshifts, find physically similar galaxies; and (4) stellar masses of
these LBGs are directly proportional to their UV luminosities with a
logarithmic slope of ~0.46, and star-formation rates are proportional to their
stellar masses with a logarithmic slope of ~0.90. These relations hold true ---
within luminosities probed in this study --- for LBGs from z~1.5 to 5. The
star-forming galaxies selected using other color-based techniques show similar
correlations at z~2, but to avoid any selection biases, and for direct
comparison with LBGs at z>3, a true Lyman break selection at z~2 is essential.
The future HST UV surveys, both wider and deeper, covering a large luminosity
range are important to better understand LBG properties, and their evolution.Comment: Accepted for publication in ApJ (29 pages, 9 figures
The XMM-Newton serendipitous ultraviolet source survey catalogue
The XMM-Newton Serendipitous Ultraviolet Source Survey (XMM-SUSS) is a
catalogue of ultraviolet (UV) sources detected serendipitously by the Optical
Monitor (XMM-OM) on-board the XMM-Newton observatory. The catalogue contains
ultraviolet-detected sources collected from 2,417 XMM-OM observations in 1-6
broad band UV and optical filters, made between 24 February 2000 and 29 March
2007. The primary contents of the catalogue are source positions, magnitudes
and fluxes in 1 to 6 passbands, and these are accompanied by profile
diagnostics and variability statistics. The XMM-SUSS is populated by 753,578 UV
source detections above a 3 sigma signal-to-noise threshold limit which relate
to 624,049 unique objects. Taking account of substantial overlaps between
observations, the net sky area covered is 29-54 square degrees, depending on UV
filter. The magnitude distributions peak at 20.2, 20.9 and 21.2 in UVW2, UVM2
and UVW1 respectively. More than 10 per cent of sources have been visited more
than once using the same filter during XMM-Newton operation, and > 20 per cent
of sources are observed more than once per filter during an individual visit.
Consequently, the scope for science based on temporal source variability on
timescales of hours to years is broad. By comparison with other astrophysical
catalogues we test the accuracy of the source measurements and define the
nature of the serendipitous UV XMM-OM source sample. The distributions of
source colours in the UV and optical filters are shown together with the
expected loci of stars and galaxies, and indicate that sources which are
detected in multiple UV bands are predominantly star-forming galaxies and stars
of type G or earlier.Comment: Accepted for publication in MNRA
Hubble Space Telescope Imaging of Lyman Alpha Emission at z=4.4
We present the highest redshift detections of resolved Lyman alpha emission,
using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in
parallel with the Wide Field Camera 3 Early Release Science program in the
GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically
confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the
sample of LAEs with resolved Lyman alpha emission. Comparing the light
distribution between the rest-frame ultraviolet continuum and narrowband
images, we investigate the escape of Lyman alpha photons at high redshift.
While our data do not support a positional offset between the Lyman alpha and
rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out
of the three galaxies are significantly larger in Lyman alpha than in the
rest-frame UV continuum. This result is confirmed when comparing object sizes
in a stack of all objects in both bands. Additionally, the narrowband flux
detected with HST is significantly less than observed in similar filters from
the ground. These results together imply that the Lyman alpha emission is not
strictly confined to its indigenous star-forming regions. Rather, the Lyman
alpha emission is more extended, with the missing HST flux likely existing in a
diffuse outer halo. This suggests that the radiative transfer of Lyman alpha
photons in high-redshift LAEs is complicated, with the interstellar-medium
geometry and/or outflows playing a significant role in galaxies at these
redshifts.Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figure
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